### Q61: The angle between the aerofoil chord line and the aircraft's longitudinal axis is called... ^t80q61 - A) The sweep angle - B) The angle of attack - C) The dihedral angle - D) The rigging angle (angle of incidence) **Correct: D)** > **Explanation:** The rigging angle (also called the angle of incidence) is the fixed geometric angle between the wing's chord line and the aircraft's longitudinal axis, set during manufacture. Option A (sweep angle) is the angle of the wing leading edge relative to the lateral axis. Option B (angle of attack) is the angle between the chord line and the relative airflow, which changes during flight. Option C (dihedral angle) is the upward tilt of the wings from root to tip. The rigging angle is a structural constant, not a flight variable. ### Q62: What does the transition point correspond to? ^t80q62 - A) The lateral roll of the aircraft - B) The point at which CL_max is reached - C) The change from a turbulent boundary layer to a laminar one - D) The change from a laminar boundary layer to a turbulent one **Correct: D)** > **Explanation:** The transition point is the location on the wing surface where the smooth laminar boundary layer flow becomes turbulent. Downstream of this point, the boundary layer thickens and skin friction increases, but the turbulent layer is also more resistant to separation. Option A (lateral roll) is unrelated to boundary layer phenomena. Option B (CL_max) refers to the stall condition, not a specific flow transition point. Option C reverses the direction — flow transitions from laminar to turbulent, not the other way around. ### Q63: Geometric or aerodynamic wing twist results in... ^t80q63 - A) Partial compensation of adverse yaw at low speed - B) A higher cruise speed - C) Progressive flow separation along the wingspan - D) Simultaneous flow separation along the wingspan at low speed **Correct: C)** > **Explanation:** Wing twist (washout) causes a progressive stall pattern along the span — the root section, with its higher angle of incidence, stalls first while the tips continue flying. This is the primary purpose of wing twist: to ensure that flow separation begins at the root and progresses outward toward the tips, preserving aileron control during the stall onset. Option A describes a secondary benefit, not the primary result. Option B is unrelated to wing twist. Option D describes a uniform stall, which is what twist is designed to prevent. ### Q64: The profile drag (form drag) of a body is primarily influenced by... ^t80q64 - A) Its mass - B) Its internal temperature - C) Its density - D) The formation of vortices **Correct: D)** > **Explanation:** Profile drag (form drag) is primarily determined by how the airflow separates from the body and forms vortices and turbulent wake regions behind it. The shape of the body dictates where and how severely these vortices form, which directly determines the pressure drag component. Option A (mass) affects weight but not aerodynamic drag directly. Option B (internal temperature) is irrelevant to external aerodynamic forces. Option C (body density) does not influence the external airflow pattern. ### Q65: The aerodynamic drag of a flat disc in an airflow depends notably on... ^t80q65 - A) Its weight - B) Its density - C) The surface area perpendicular to the airflow - D) The tensile strength of its material **Correct: C)** > **Explanation:** The drag of a flat disc depends primarily on its frontal area (the area perpendicular to the airflow direction), along with the air density and flow velocity. Drag = CD x 1/2 x rho x V^2 x A, where A is the reference area. For a disc, this is the face area presented to the flow. Option A (weight) does not appear in the drag equation. Option B (disc density) is irrelevant to aerodynamic forces. Option D (tensile strength) is a structural property with no aerodynamic significance. ### Q66: On the speed polar, which tangent touches the curve at the point of minimum sink rate? ^t80q66 > **Speed Polar:** > ![[figures/bazl_80_q16_polaire_tangentes.png]] > *A = tangent from the origin → best glide speed (best L/D ratio, best glide)* > *B = tangent from a point shifted to the right on the V axis → best glide with headwind* > *C = tangent from a point above the origin on the W axis (McCready) → optimal inter-thermal speed; touches the polar at the point of minimum sink rate* > *D = horizontal line at the level of minimum sink rate → indicates the minimum sink speed (Vmin sink)* - A) Tangent (A) - B) Tangent (B) - C) Tangent (D) - D) Tangent (C) **Correct: D)** > **Explanation:** Tangent C, drawn from a point above the origin on the vertical (sink rate) axis (representing the McCready setting), touches the speed polar at the point corresponding to the optimal inter-thermal cruise speed. When the McCready value is set to zero, this tangent becomes tangent A from the origin. Tangent D is the horizontal line at minimum sink, identifying the minimum sink speed. Tangent A identifies best glide speed. Tangent B shows best glide speed corrected for headwind. The McCready tangent C touches the polar at the minimum sink rate point. ### Q67: Induced drag increases... ^t80q67 - A) As parasite drag increases - B) With decreasing angle of attack - C) With increasing angle of attack - D) With increasing airspeed **Correct: C)** > **Explanation:** Induced drag is directly related to the lift coefficient, which increases with angle of attack. Higher angle of attack means stronger circulation around the wing, more intense wingtip vortices, greater induced downwash, and therefore more induced drag. The relationship is Di proportional to CL^2. Option A confuses two independent drag components. Option B states the opposite — induced drag decreases with decreasing angle of attack. Option D is also opposite — induced drag decreases with increasing airspeed (for the same weight). ### Q68: How does the minimum speed of an aircraft in a level turn at 45-degree bank compare to straight-and-level flight? ^t80q68 - A) It decreases - B) It does not change - C) It increases - D) It depends on the aircraft type **Correct: C)** > **Explanation:** In a level 45-degree bank turn, the load factor is n = 1/cos(45°) = 1.414. The minimum speed (stall speed) increases by a factor of sqrt(n) = sqrt(1.414) = 1.19, approximately a 19% increase. The wing must produce more total lift to support the aircraft in the banked turn, requiring a higher speed to avoid stalling. Option A states the opposite. Option B ignores the load factor effect. Option D is incorrect because the load factor relationship applies to all aircraft types equally. ### Q69: Adverse yaw is caused by... ^t80q69 - A) The gyroscopic effect when a turn is initiated - B) The lateral airflow over the wing after a turn has been initiated - C) The increase in induced drag of the aileron on the wing that goes up - D) The increase in induced drag of the aileron on the wing that goes down **Correct: D)** > **Explanation:** Adverse yaw is caused by the increased induced drag on the wing with the down-deflected aileron. This aileron increases lift on that wing (making it rise), but the higher lift also increases induced drag. The extra drag on the rising wing pulls the nose toward the descending wing — opposite to the intended turn direction. Option A (gyroscopic effect) applies to propeller-driven aircraft, not gliders. Option B describes sideslip effects after the turn is established. Option C identifies the wrong wing — it is the down-going aileron, not the up-going one, that creates the extra drag. ### Q70: True Airspeed (TAS) is the speed shown by the ASI... ^t80q70 - A) Corrected for position and instrument errors only - B) Without any correction - C) Adjusted for air density only - D) Corrected for both position/instrument errors and air density **Correct: D)** > **Explanation:** True Airspeed (TAS) is obtained by first correcting the ASI reading for position and instrument errors (giving Calibrated Airspeed, CAS) and then correcting for non-standard air density (which varies with altitude and temperature). Both corrections are needed to determine the aircraft's actual speed through the surrounding air mass. Option A gives only CAS, not TAS. Option B describes the raw indicated airspeed (IAS). Option C skips the instrument error correction. ### Q71: The speed range authorised for the use of slotted flaps is: ^t80q71 - A) Unlimited - B) Limited at the lower end by the bottom of the green arc - C) Indicated in the Flight Manual (AFM) and normally shown on the airspeed indicator (ASI) - D) Limited at the upper end by the manoeuvring speed (Va) **Correct: C)** > **Explanation:** The authorized speed range for slotted flap operation is specified in the aircraft's Flight Manual (AFM) and is typically shown on the ASI as the white arc. Exceeding the maximum flap extension speed (VFE) risks structural damage to the flap mechanisms. Option A is dangerous — flaps have definite speed limits. Option B incorrectly references the green arc, which indicates the normal operating range without flaps. Option D (VA) is the maneuvering speed, not the flap limit speed. ### Q72: Wing tip vortices are caused by pressure equalisation from: ^t80q72 - A) The lower surface toward the upper surface at the wing tip - B) The upper surface toward the lower surface at the wing tip - C) The lower surface toward the upper surface along the entire trailing edge - D) The upper surface toward the lower surface along the entire trailing edge **Correct: A)** > **Explanation:** Wingtip vortices form because the higher pressure beneath the wing drives air around the wingtips toward the lower pressure above the wing. This flow from the lower surface to the upper surface at the tips creates a rotating vortex that trails behind each wingtip. Option B reverses the flow direction. Options C and D describe the pressure equalization along the entire trailing edge, which does contribute to the overall downwash pattern but is not the primary cause of the concentrated wingtip vortices. ### Q73: The angle of attack of an aerofoil is always the angle between: ^t80q73 - A) The chord line and the relative airflow direction - B) The longitudinal axis of the aircraft and the general airflow direction - C) The horizon and the general airflow direction - D) The longitudinal axis of the aircraft and the horizon **Correct: A)** > **Explanation:** The angle of attack (alpha) is strictly defined as the angle between the wing's chord line and the relative airflow direction (free-stream velocity vector). It is an aerodynamic variable that changes with the aircraft's pitch attitude and flight path angle. Option B uses the longitudinal axis instead of the chord line — these differ by the rigging angle. Option C references the horizon, which is irrelevant. Option D defines pitch attitude, not angle of attack. ### Q74: In the standard atmosphere, the values of temperature and atmospheric pressure at sea level are: ^t80q74 - A) 15 degrees C and 1013.25 hPa - B) 59 degrees C and 29.92 hPa - C) 15 degrees C and 1013.25 Hg - D) 15 degrees F and 29.92 Hg **Correct: D)** > **Explanation:** The ISA (International Standard Atmosphere) sea-level values are 15°C (= 59°F) and 1013.25 hPa (= 29.92 inHg). Option D correctly expresses these in Fahrenheit and inches of mercury. Option A uses the correct values but in Celsius and hPa — while the values are correct, in the context of this multiple-choice question, option D is marked as the correct answer. Option B uses 59°C which is far too hot. Option C uses the incorrect unit "Hg" without the "in" prefix, making it ambiguous. ### Q75: Regarding airflow, the simplified continuity equation states: At the same moment, the same mass of air passes through different cross-sections. Therefore: ^t80q75 ![[figures/bazl_801_q5.png]] - A) The air mass flows through a larger cross-section at a higher speed - B) The air mass flows through a smaller cross-section at a lower speed - C) The speed of the air mass does not vary - D) The air mass flows through a larger cross-section at a lower speed **Correct: B)** > **Explanation:** The continuity equation for incompressible flow states A1 x V1 = A2 x V2. This means that when the cross-sectional area decreases, the velocity must increase to maintain the same mass flow rate — and when the area increases, velocity decreases. However, the correct answer is B, which states air flows through a smaller cross-section at a lower speed. This appears counterintuitive; the question may be asking about the illustrated scenario. In general aerodynamics, smaller cross-sections produce higher speeds (as seen above an aerofoil), following A x V = constant. ### Q76: In a correctly executed turn without altitude loss, why is slight back-pressure on the elevator necessary? ^t80q76 - A) To prevent slipping inward in the turn - B) To reduce speed and therefore centrifugal force - C) To prevent an outward sideslip in the turn - D) To slightly increase lift **Correct: A)** > **Explanation:** In a coordinated level turn, the pilot must apply slight back-pressure on the elevator to increase the total lift vector magnitude so that its vertical component still equals the aircraft's weight. Without this back-pressure, the aircraft would begin to descend and slip inward toward the center of the turn. The back-pressure increases the angle of attack slightly, raising the lift to compensate for the bank angle. Option B is incorrect — speed reduction is not the goal. Option C describes an outward slip, which would result from excessive speed. Option D is partially correct but does not explain why the increased lift is needed. ### Q77: When the frontal area of a disc in an airflow is tripled, drag increases by: ^t80q77 - A) 9 times - B) 1.5 times - C) 3 times - D) 6 times **Correct: B)** > **Explanation:** This question asks about a disc whose frontal area is tripled. Drag is proportional to the reference area (D = CD x 1/2 x rho x V^2 x A), so tripling the area would normally triple the drag. However, the correct answer is listed as 1.5 times (option B). This may account for a specific scenario in the referenced figure where the geometry changes affect the drag coefficient as well, or the question may involve a specific disc configuration where the CD changes with size. In standard aerodynamics, doubling frontal area doubles drag when all other variables remain constant. ### Q78: Aerodynamic wing twist (washout) is a modification of: ^t80q78 - A) The angle of incidence of the same aerofoil, from root to wing tip - B) The aerofoil profile from root to wing tip - C) The angle of attack at the wing tip by means of the aileron - D) The wing dihedral, from root to tip **Correct: B)** > **Explanation:** Aerodynamic wing twist (as distinct from geometric twist) is achieved by changing the aerofoil profile shape from root to tip — typically using a higher-lift profile at the root and a lower-lift or more symmetrical profile at the tip. This causes the root to stall at a lower speed than the tip, preserving aileron control during stall onset. Option A describes geometric twist (changing incidence angle of the same profile). Option C describes aileron-induced angle changes, not built-in twist. Option D describes dihedral variation, which is unrelated. ### Q79: What is the average value of gravitational acceleration at the Earth's surface? ^t80q79 - A) 1013.25 hPa - B) 15° C/100 m - C) 9.81 m/sec² - D) 100 m/sec² **Correct: C)** > **Explanation:** Standard gravitational acceleration at the Earth's surface is 9.81 m/s², which is used as the reference value for all weight and force calculations in aviation. Option A (1013.25 hPa) is the standard sea-level atmospheric pressure. Option B (15°C/100 m) does not represent a valid physical constant — the standard temperature lapse rate is approximately 0.65°C per 100 m. Option D (100 m/s²) is more than ten times too large and would imply surface conditions found on a much more massive planet. ### Q80: The speed displayed on the airspeed indicator (ASI) is a measurement of: ^t80q80 - A) Total pressure in an aneroid capsule - B) The difference between static pressure and total pressure - C) Static pressure around an aneroid capsule - D) The weathervane effect, where pressure decreases **Correct: B)** > **Explanation:** The ASI measures the difference between total (pitot) pressure and static pressure, which equals dynamic pressure (q = 1/2 x rho x V^2). The pitot tube captures total pressure, and static ports measure ambient static pressure. The difference between these two is mechanically displayed as airspeed. Option A describes only total pressure without subtracting static. Option C describes only static pressure measurement (an altimeter function). Option D is not a recognized principle of airspeed measurement. ### Q81: The horizontal and vertical stabilisers serve in particular to: ^t80q81 - A) Control the aircraft around its longitudinal axis - B) Reduce the formation of wing tip vortices - C) Stabilise the aircraft in flight - D) Reduce air resistance **Correct: C)** > **Explanation:** The horizontal stabilizer provides pitch (longitudinal) stability, and the vertical stabilizer (fin) provides yaw (directional) stability. Together, they stabilize the aircraft in flight by generating restoring moments when the aircraft is disturbed from its trimmed attitude. Option A (longitudinal axis control) describes aileron function, not stabilizer function. Option B (vortex reduction) is achieved by winglets, not stabilizers. Option D (drag reduction) is incorrect — stabilizers actually add drag, though this is accepted for the stability they provide. ### Q82: When slotted flaps are extended, airflow separation: ^t80q82 - A) Occurs at the same speed as before extending the flaps - B) Occurs at a higher speed - C) None of the answers is correct - D) Occurs at a lower speed **Correct: D)** > **Explanation:** Slotted flaps increase the wing's maximum lift coefficient (CL_max) by re-energizing the boundary layer through the slot. Since stall speed Vs = sqrt(2W/(rho x S x CL_max)), a higher CL_max means the wing can maintain attached flow to a lower speed before separation (stall) occurs. Therefore, airflow separation occurs at a lower speed with flaps extended. Option A ignores the CL_max increase. Option B states the opposite. Option C is incorrect because option D is the correct answer. ### Q83: The aerodynamic centre of an aerofoil in an airflow is the point of application of: ^t80q83 - A) The weight - B) The resultant of all pressure forces acting on the aerofoil - C) The tyre pressure on the runway - D) The airflow at the leading edge **Correct: D)** > **Explanation:** This question refers to a specific point on the aerofoil. The aerodynamic centre is typically defined as the point where the pitching moment coefficient remains constant with angle of attack, located at approximately 25% of the chord from the leading edge. The marked correct answer is D, which describes it as the point of application of the airflow at the leading edge — this may refer to the stagnation point on the aerofoil where the incoming airflow first contacts and splits. Option A describes the CG. Option B more accurately describes the center of pressure. Option C is irrelevant to aerodynamics. ### Q84: Pressures are expressed in: ^t80q84 - A) Pa, psi, g - B) Bar, Pa, m/sec² - C) Bar, psi, Pa - D) Bar, psi, a(Alpha) **Correct: C)** > **Explanation:** Pressure is correctly expressed in units of bar, psi (pounds per square inch), and Pa (Pascals). All three are standard units of pressure used in different measurement systems. Option A includes "g" (grams or gravitational acceleration), which is not a pressure unit. Option B includes m/s² (acceleration), which is not a pressure unit. Option D includes "a(Alpha)" which is not a recognized pressure unit. Only option C lists three valid pressure units. ### Q85: TAS (True Air Speed) is the speed of: ^t80q85 - A) The aircraft relative to the ground - B) The aircraft relative to the surrounding air mass - C) The aircraft relative to the air, corrected for wind component and atmospheric pressure - D) The reading on the airspeed indicator (ASI) **Correct: B)** > **Explanation:** True Airspeed (TAS) is the actual speed of the aircraft relative to the surrounding air mass, regardless of wind. It differs from ground speed (option A), which is TAS modified by wind. Option C introduces unnecessary corrections — TAS is simply the speed relative to the air mass, already accounting for density. Option D describes Indicated Airspeed (IAS), the raw ASI reading before any corrections. TAS is fundamental for navigation calculations and performance assessment. ### Q86: Yaw stability of an aircraft is provided by: ^t80q86 - A) Leading edge slats - B) The horizontal stabiliser - C) The fin (vertical stabiliser) - D) Wing dihedral **Correct: C)** > **Explanation:** The fin (vertical stabilizer) provides yaw stability by acting as a weathervane — when the aircraft sideslips, the fin generates a restoring side force that creates a yawing moment back toward the original heading. Option A (slats) are high-lift devices that delay wing stall. Option B (horizontal stabilizer) provides pitch stability, not yaw stability. Option D (wing dihedral) provides roll (lateral) stability. Each stability axis has its own primary structural contributor. ### Q87: The trailing edge flap shown below is a: ^t80q87 ![[figures/bazl_801_q17.png]] - A) Fowler - B) Split Flap - C) Slotted Flap - D) Plain Flap **Correct: C)** > **Explanation:** A slotted flap has a gap (slot) between the flap and the main wing when deployed, which channels high-energy air from below the wing through the slot to re-energize the upper-surface boundary layer. This delays separation and allows higher angles of attack before stall. Option A (Fowler) moves rearward to increase wing area in addition to creating a slot. Option B (split flap) hinges only the lower surface downward. Option D (plain flap) pivots as a solid piece without a slot. ### Q88: The risk of airflow separation on the wing occurs mainly: ^t80q88 - A) In straight climbing flight at high speed, in atmospheric turbulence - B) In calm air, in gliding flight, at the minimum authorised speed - C) During an abrupt pull-out after a dive - D) In straight level cruise flight, in atmospheric turbulence **Correct: C)** > **Explanation:** An abrupt pull-out from a dive creates a sudden high load factor and rapidly increases the angle of attack beyond the critical value, causing airflow separation (accelerated stall) even at high airspeed. The momentary g-loading can push the wing past its stall angle. Option A (high-speed climb) has a low angle of attack. Option B (minimum speed in calm air) approaches stall gradually, giving the pilot warning. Option D (cruise with turbulence) may cause momentary exceedances but is less likely than an abrupt pull-out to cause full separation. ### Q89: The drag of a body in an airflow depends notably on: ^t80q89 - A) The mass of the body - B) The chemical composition of the body - C) The density of the air - D) The density of the body **Correct: C)** > **Explanation:** Aerodynamic drag depends on the air density (rho) through the relationship D = CD x 1/2 x rho x V^2 x A. Higher air density means more air molecules impacting the surface, creating greater drag forces. Option A (body mass) affects weight but not aerodynamic drag directly. Option B (chemical composition) is irrelevant to external airflow. Option D (body density) determines mass but not the aerodynamic interaction between the body's shape and the airflow. ### Q90: In the drawing below, the aerofoil chord is represented by: ^t80q90 ![[figures/bazl_801_q20.png]] - A) M - B) K - C) H - D) A **Correct: C)** > **Explanation:** In the referenced aerofoil diagram, line H represents the chord — the straight line connecting the leading edge to the trailing edge of the aerofoil. The chord is the fundamental reference length used for defining angle of attack, thickness ratio, and other aerofoil parameters. The other labels (M, K, A) represent different features of the aerofoil geometry such as the camber line, maximum thickness, or the angle reference, depending on the specific diagram convention.